Best way to cast values?

[mhkeller]

Let's say I'm reading in a csv and I want to cast some fields from strings to numbers, is there an arquero-y way of doing this? Or should I do my regular looping through of the data before calling aq.from(data)? I'm not sure if calling .derive with the same column name as an existing one is an okay practice. Seems a little confusing semantically.

It would be neat if there was a verb like .cast that took a column name and a JavaScript type. It could have some error handling too or a predicate that determines what to do if, say, you have a NaN value.

aq.from(data)
  .cast('my-column', 'number', d => op.is_nan(d) ? null : d)